But in his rollicking new book “Star: How Warren Beatty Seduced America” (Simon & Schuster), biographer Peter Biskind hazards a guess about the conquests of Hollywood’s most notorious lothario — based, he says, on “simple arithmetic.”

Biskind estimates “12,775 women, give or take, a figure that does not include daytime quickies, drive-bys, casual gropings, stolen kisses and so on.”

As it turns out, the “Bonnie and Clyde” star was a late bloomer and didn’t lose his virginity until he was almost 20 — but he would make up for lost time in the decades to follow, bedding just about every woman on Hollywood’s ever-changing A-list, as well as any other woman who happened to, literally, cross paths with him.

Beatty has never been a kiss-and-tell guy, though. To the immense frustration of interviewers over the years, writes Biskind, “even when he appears to be saying something, he is saying nothing.”

But Biskind, a longtime Hollywood writer, formed a surprising friendship with the actor — and, at 72, Beatty finally agreed to an authorized biography, dishing on his long list of leading ladies:

JANE FONDA

When a young Beatty auditioned for a teen movie, “Parrish,” in 1960, his scene partner was a fresh-faced actress named Jane Fonda.

On the first take, Beatty gave her a brief, chaste kiss. “I thought he was gay,” Fonda tells Biskind. Director Joshua Logan was not having it. “Look, are you afraid of Jane or something? Grab her, boy, grab her. Don’t be shy.” It was a directive that Beatty would apply to his love life forever after. “Oh, my God. We kissed until we had practically eaten each other’s heads off,” Beatty tells Biskind.

The two went on to become an item, and Beatty would later rave about Fonda’s sexual prowess “due to her ability to virtually unhinge her jaw, like a python that swallows prey much larger than itself.”

JOAN COLLINS

As Fonda remembers it, she and Beatty were dining at Beverly Hills restaurant La Scala when her boyfriend spotted British actress Joan Collins across the room. As Collins was moping about her fading affair with Cloris Leachman’s producer husband, she “noticed the indecently pretty young man boldly eyeing her from a nearby table. He was 22 at the time, but he looked like he was barely old enough to drive.”

Beatty dropped Fonda for Collins, and the two became an inseparable, insatiable couple. “He made love to [Joan] Collins relentlessly,” Biskind writes. “But for Collins, it was too much of a good thing. One Sunday morning, exhausted, she stumbled out of bed. Dragging on a forbidden cigarette, she said, ‘I don’t think I can last much longer. He never stops — it must be all those vitamins he takes . . . In a few years, I’ll be worn out.’ Later, a skeptic asked her if they really had sex seven times a day. She replied, ‘Maybe he did, but I just lay there.’ ”

SHIRLEY MacLAINE

Beatty’s older sister was an early contender for the role of Bonnie in “Bonnie and Clyde” — that is, until her brother began to think about starring in the film as well as producing it.

“With Beatty starring, MacLaine was out,” Biskind writes. “She quipped, ‘That would be adding incest to injury.’ Beatty was unamused by her attempts at humor at his expense. As in, ‘I’d love to do a kissing scene with him, to see what all the fuss is about . . . I keep my daughter as far away from Warren as possible!’ ”

JULIE CHRISTIE

When Beatty first spotted the gorgeous English actress, it was in 1965, and she was an Oscar contender for her lead role in “Darling.” As actress Leslie Caron, another of Beatty’s longtime loves, observes to Biskind, “Warren has an interesting psychology. He always falls in love with girls who have won or been nominated for an Academy Award.”

Beatty and Christie had a long, passionate, often turbulent relationship — mostly due to Beatty’s chronic inability to be faithful. When he was shooting 1974’s “The Parallax View,” for example, his trailer had a steady stream of female admirers coming and going. An intern on the film recalled being surprised that “some of the girls outside Beatty’s trailer who got past the door were not particularly attractive, especially since Julie Christie, who was doing ‘Uncle Vanya’ on Broadway, was flying in to spend every weekend with him. Some were chubby, some had hints of mustaches on their upper lips. Some had the errant pimple or mole or other blemishes.”

Beatty was an equal-opportunity seducer, Biskind writes, who would have sex at the drop of a hat and for an ever-expanding number of reasons. “Late in 1971, he implored singer-songwriter Carole King, who was pregnant at the time, to sleep with him because, he explained, he’d never been with a late-term woman and wanted to see what it was like. (She refused.) One night he got a phone call from a woman he didn’t remember, who was married and lived in Colorado. She’d had breast cancer and a mastectomy. Her husband didn’t want to sleep with her anymore. Beatty was outraged, told her ‘I’d f- – – you in a second. Fly out here.’ ”

DIANE KEATON

In keeping with Caron’s Oscar scorecard, Beatty’s interest in actress Diane Keaton perked up right after she won Best Actress for 1977’s “Annie Hall.”

“I wasn’t the Warren Beatty type, but there I was,” Keaton tells Biskind. “He was just so . . . overwhelming in every way. I remember looking at his face and going, ‘How am I here with this?’ The brilliance and the talent, you get caught up in it.”

Keaton went on to play the role of Louise Bryant in Beatty’s film “Reds,” where his more controlling side came out during one audition, writes Biskind. “George Plimpton, who was offered the part of a lecherous publisher [in ‘Reds’] after he literally tripped over Beatty asleep on the floor of the Playboy Mansion, auditioned for it by kissing Keaton with so much conviction that Beatty yelled, ‘Stop it.’ ”

The combination of Beatty’s charm and his compulsive need to be in control would surface with many subsequent lovers — such as actress Joyce Hyser, who ended up in therapy because of him.

“Her therapist always told her that her relationship with Beatty was a mistake,” Biskind writes. “He would say, ‘You gotta get outta there, you gotta break it off, it’s not right for you.’ Beatty, who was a therapy junkie, wanted to join her. She recalls, ‘Within 10 minutes, Warren had completely taken over the session. My therapist was saying to me, “Why do you feel you need to leave?” My therapist was totally in love with him.’ ”

FRAN DRESCHER

The nasal-voiced star of “The Nanny” read for a small role in Beatty’s famous 1987 flop, “Ishtar,” and recalls one colorful exchange with the actor, who was sleeping with the film’s star, Isabelle Adjani. “He offered to introduce her to Adjani, saying, ‘We were both talking about you while lying in bed last night.’ Adjani told her, ‘You are very beautiful.’ But it wasn’t until Beatty added, ‘We were both hoping you would like to join us for dinner this evening, just the three of us,’ that the flashbulb went off: ‘I sure as hell knew a ménage-à-troiserino when I saw one,’ she thought.” Drescher turned down the offer.

JANICE DICKINSON

The wild-child supermodel ended up in Beatty’s hotel room and tells Biskind she went to bed with the actor but woke up alone in the middle of the night. “I looked across the room and found him admiring himself in the mirror . . . In the morning, when I woke up, he was standing there again, playing with his hair, mussing it; trying to get it just right — going for that just-been-f- – -ed look.”

MADONNA

When Beatty cast Madonna in the role of Breathless Mahoney in 1990’s “Dick Tracy,” which he was both directing and starring in, he locked onto the pop star as his latest conquest. She turned out to be more than he bargained for.

Nightclub-loving Madonna would drag Beatty out to the gay discos with her, and try unsuccessfully to get him to dance (“Hey, P- – -y Man, come on out here”) while pals like Sandra Bernhard hung around and made fun of him. “We would taunt him, say things to make him uncomfortable. In a loving way. He was a perfect target, because he played the befuddled old man with her: ‘Wha?’ ‘Huh?’ ‘What’s all this craziness?’ The whole relationship was a performance.”

“Beatty, a man who was accustomed to being worshipped by women, was on dangerous ground with Madonna,” Biskind writes. “Why he sat still for this kind of treatment remains a mystery. Chances are, he was taking his own advice. He would tell director Glenn Gordon Caron a few years later, ‘Never, ever f- – – your leading lady. And if you do, don’t stop till the picture’s finished.’ ”

ANNETTE BENING

Barry Levinson’s 1991 movie “Bugsy” is probably best known as the movie that domesticated Warren Beatty. His first meeting with actress Annette Bening, who was vying for a role in the film, made an impression on “Bugsy” screenplay writer James Toback, now a director.

“He let out this growl . . . A primordial yelp of love, lust, desire, enthusiasm, a sound that one would expect a starving man to make at the prospect of finally being able to devour a huge and delicious meal. I realized that without question the role was already now settled,” Toback tells the author.

The rest is history. How did Bening succeed in taming the actor where so many others had failed? Beatty himself offered a possible explanation to a former girlfriend, actress Delaune Michel. “I think back sometimes on a few of the women who were in my life before, the ones my mind naturally wanders to, the heavyweights, like you. I could have married any one of you and been happy. There isn’t just one true love for anyone; timing is everything.”

‘I don’t think I can last much longer. He never stops — it must be all those vitamins he takes . . . In a few years I’ll be worn out.’

– Joan Collins

‘He let out this growl. . . A primordial yelp of love, lust, desire, enthusiasm, a sound that one would expect a starving man to make at the prospect of finally being able to devour a huge and delicious meal.’